A circuit breaker is an overcurrent protective device that is used for circuit protection and isolation. The circuit breaker provides electrical system protection when a designated electrical abnormality such as an overcurrent or overload event occurs in the system. One type of circuit breaker is a miniature circuit breaker (MCB), which is typically used for low voltage applications. An MCB typically includes a base and cover, and an electrical circuit between a line terminal and a load terminal. The electrical circuit includes a conductive stationary contact electrically connected to one of the terminals and a movable contact electrically connected to the other terminal. The movable contact is secured on a movable blade (also referred to as a contact carrier). A handle assembly, in the form of a single piece handle, interfaces with the blade and the trip lever of the trip mechanism as further explained below. The handle assembly can be operated by a user to move the blade, and thus the movable contact, between an open position and a closed position to open or close the electrical circuit. In the closed position, the movable contact is engaged with the stationary contact to allow current flow between the two contacts to a protected load. In the open position, the movable contact is disengaged from the stationary contact to prevent or interrupt current flow to the protected load.
The MCB also includes a trip mechanism. The trip mechanism controls a trip lever, which is connected to the blade via a tension spring (also known as a “toggle spring”). When an abnormal operating condition is detected (e.g., an over current or over temperature fault), the trip mechanism implements a trip operation to disengage the movable contact from the stationary contact by releasing or unlatching the trip lever, which in turn interrupts current flow to the protected load at another open position generally referred to as the tripped position. Thereafter, the circuit breaker can be reset to an intermediate or reset position, and then returned to an open position. Once in the open position, the user can move the breaker back to the closed position via the handle assembly.
A miniature circuit breaker is subject to size constraints. As a consequence, there is very little space to arrange and fit the numerous moving parts of the breaker in the cover and base, thereby creating design restrictions as to the size, shape, dimension and materials of the various parts of the breaker. For example, in one type of MCB, the single piece handle, which is directly interfaced to the movable blade, is constantly subjected to the force of the tension spring, and thus, is subject to greater wear from the operation of the circuit breaker (e.g., a circuit breaker is typically switched mechanically and electrically over 10,000 times to comply with testing requirements). The single piece handle is connected to the metallic movable blade, and thus, must have sufficient durability, strength and/or rigidity to provide a suitable plastic to metal interface between the handle and the blade. Therefore, the single piece handle must be constructed with a significant thickness using a rigid or strong non-conductive material, such as thermoset.
Furthermore, in certain types of MCBs, the top portion of the tension spring, which is connected to the trip lever, is designed without coils (e.g., a partially coiled tension spring) in order to avoid becoming entangled with a portion of the handle. The use of a partially coiled tension spring is inefficient and costly, since the coils must be designed to provide a greater force (to compensate for the non-coiled portion) than otherwise would be needed if a fully coiled tension spring is used. Furthermore, the thickness of the handle also impacts the design of the trip lever and other components such as the blade in an area in the MCB where potential interference between the parts may occur, e.g., an interference area.
Accordingly, there is a need for a practical and reliable solution for providing greater flexibility in the design and assembly of the various parts of a circuit breaker, particularly a MCB. There is also a need to improve upon the durability of the handle of an MCB.